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NDA 2025
Exam
NDA
Year
2025
Subject
Mathematics
Chapter
Basics of Mathematics

NDA 2025 · Mathematics · Basics of Mathematics

If p^x = q^y = r^z , where x , y and z are in GP, then consider the...

If px=qy=rzp^x = q^y = r^z, where xx, yy and zz are in GP, then consider the following statements:
I. pp, qq and rr are in AP.
II. ln⁡p\ln p, ln⁡q\ln q and ln⁡r\ln r are in GP.
Which of the statements given above is/are correct?

Options

  1. AI only
  2. BII only
  3. CBoth I and II
  4. DNeither I nor II

Correct answer

B. II only

Step-by-step solution

Let px=qy=rz=kp^x = q^y = r^z = k

Taking natural logarithm on all sides:

xln⁡p=yln⁡q=zln⁡r=ln⁡kx \ln p = y \ln q = z \ln r = \ln k

x=ln⁡kln⁡px = \dfrac{\ln k}{\ln p}, y=ln⁡kln⁡qy = \dfrac{\ln k}{\ln q}, z=ln⁡kln⁡rz = \dfrac{\ln k}{\ln r}

Since xx, yy, and zz are in GP, y2=xzy^2 = xz

Substituting the values of xx, yy, and zz:

\left( \dfrac{\ln k}{\ln q} \right)^2 = \left( \dfrac{\ln k}{\ln p} \right)\left( \dfrac{\ln k}{\ln r} \right)<br><br><br><br>\dfrac{1}{(\ln q)^2} = \dfrac{1}{\ln p \ln r}<br><br><br><br>(\ln q)^2 = \ln p \ln r<br><br>Thisimpliesthat<br><br>This implies that\ln p,,\ln q,and, and\ln r$ are in GP.

Statement II is correct, while Statement I is not necessarily true.

Answer: II only
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